When water isn’t enough, and how to choose the right form of minerals.
When it’s hot or you’re training for longer than an hour, water alone is often not enough. You lose electrolytes through sweat (mainly sodium, but also potassium and magnesium), which leads to a drop in performance, cramps and a slowdown in pace. This post is a short, practical guide: when to reach for an isotonic drink, how to choose the right composition and which forms of minerals make sense.
TL;DR (in 30 seconds)
- The most important component in a sports drink is sodium – it helps maintain fluid balance and neuromuscular conduction.
- You should primarily get your potassium and magnesium from your diet and regular supplements (if necessary), not at the last minute before the race.
- For most people: 0.4–0.8 L of fluid per hour, containing ~500–800 mg of sodium per litre, during exercise lasting >60–90 minutes or in hot weather.
When does the water run out?
- Duration: exercise >60–90 mins
- Conditions: heat, high humidity, lack of shade/ventilation.
- On an individual basis: ‘salty sweat’, a tendency to cramp, dizziness, a marked drop in pace despite drinking water.
- 2% test: weigh yourself before and after training – a loss of more than 2% of body weight indicates insufficient fluid or electrolyte intake.
How to make an isotonic drink (a starting point)
- Sodium: ~500–800 mg/L (in ‘salty sweat’ or hot weather, up to ~1000 mg/L).
- Carbohydrates: 6–8% (60–80 g/L) – for long/intense sessions.
- Potassium: 100–200 mg/L (a supplementary element, not the main one).
- Fluids: usually 0.4–0.8 L/h; rarely >1.0–1.2 L/h (risk of sodium dilution).
Homemade recipe (1 litre):
- still water, 1 litre
- ¼ teaspoon of table salt (~1.5 g) → ~600 mg of sodium
- lemon/lime juice (flavour + vitamin C)
- sugar/honey 4–6 tablespoons (48–72 g) – you can start with 4 and adjust to taste
- optional: a pinch of potassium chloride (KCl) or 100 ml of tomato juice (a source of potassium)
Test it out during training, not on race day. Adjust the salt and sugar levels to suit your stomach.
Magnesium – what does it do and in what form?
Role: neuromuscular transmission, muscle contraction and relaxation, energy metabolism.
When should you consider taking magnesium? If your diet is deficient (low in whole grains, pulses and nuts) or if you have symptoms of deficiency confirmed by a test.
Forms that usually work well
- Citrate / bisglycinate – good bioavailability, often better tolerated.
- Malate – a popular choice for energy, well tolerated.
- Oxide – lower bioavailability, more frequent digestive problems.
Dosage (for prevention): typically 100–200 mg of magnesium ions per day, taken with a meal.
Note: taking magnesium just before a workout will not prevent cramps if they are caused by dehydration or sodium deficiency. It is really part of your daily routine, not a ‘pre-workout’ supplement.
Foods rich in magnesium: pumpkin seeds, cocoa, buckwheat, almonds, pulses, and mineral water with a high magnesium content.
Potassium – important, but be careful with supplements
Role: muscle and heart function, intracellular fluid balance.
In sport: 100–200 mg/L is sufficient in drinks – sodium is the key component in any case.
Supplements?
- If you have kidney disease or are taking potassium-sparing diuretics, ACE inhibitors or sartans, do not take supplements without consulting your doctor.
- It is better to stick to a diet consisting of: tomatoes/tomato juice, potatoes, bananas, dried apricots and pulses.
How to choose the right strategy for you (3 scenarios)
1) Training session ≤60 mins, moderate/cool
- Water is all you need. You could add a little salt if you’re sweating heavily.
2) 60–90 minutes or until warm
- 0.4–0.6 L/h of a drink containing ~500–700 mg of sodium per litre + 30–60 g of carbohydrates per hour (gels/drink).
3) >90 minutes or hot weather/high humidity
- 0.6–0.8 L/h (sometimes up to 1.0 L/h) containing ~700–1000 mg of sodium per litre + 60–90 g of carbohydrates per hour.
- Consider ways to stay cool (a cap, sponges, ice) and acclimatisation (2–7 days of gradually getting used to the heat).
The most common mistakes
- Forcing yourself to drink only water → risk of low sodium levels (hyponatraemia) and a crash.
- Not enough sodium in your water bottle → cramps, dizziness, loss of pace despite drinking.
- A new drink on race day → test the ingredients and quantities in advance.
- I believe magnesium will sort out the cramps straight away → but first sort out your sodium, fluids and pacing.
Safety
This information is intended for healthy adults. Do you have heart or kidney conditions, high blood pressure, or are you taking medication that affects your electrolyte balance? — Please consult your doctor or sports nutritionist regarding your hydration plan and supplements.
Summary
In practice: the sodium in your drink helps maintain your pace and keeps your head clear; make sure you get enough potassium and magnesium mainly through your diet and daily routine. Adjust the concentration of your drink to suit the conditions, the time of day and how much you sweat; weigh yourself before and after training and make a note of what works. Simple and effective.
Tags: #electrolytes #magnesium #potassium #hydration #isotonic #heatwave #training #cramps #sodium #endurance
